To reduce pollutants and emissions from vehicles, such as diesel engine powered truck tractors, environmental requirements have been placed on exhaust systems for such vehicles. In some systems of this type, urea from a urea storage tank is delivered to an exhaust system where it is applied as a urea dose to the exhaust to react with and reduce certain pollutants contained therein. Excess urea is returned to the storage tank for subsequent use in exhaust treatment. Under extremely cold vehicle operating conditions, it is possible for urea to freeze within the urea storage tank, making the stored urea unavailable for use in treating the exhaust. This can result in inadequate functioning of the exhaust treatment system. A temperature sensor has been used to sense the temperature of urea in the storage tank. In addition, coolant from the vehicle exhaust system, which has been warmed by the engine, has been withdrawn from the coolant system, circulated within the urea storage tank to warm and thaw a portion of the urea in the urea storage tank, with the coolant being returned to the engine coolant system. A valve remote from the storage tank has been used to control, in response to temperature signals from the temperature sensor, whether liquid from the engine coolant system is allowed to circulate through the urea storage tank. Also, urea storage tanks have been provided with a float for use as part of a level sensing circuit to provide signals indicative of the level of urea in the storage tank.
A need nevertheless exists for an improved urea storage tank system and closure member therefore.